Changes in Magnetic Flux Density Distributions of Chromium Molybdenum Steel (JIS, SCM440) by Slit Opening and Crack Growth

Non-destructive evaluation methods using magnetic measurement systems have been developed. However, there are a few approaches to the effect of cracks on magnetic fields during whole fatigue process. In the present work, slit samples of as-received chromium molybdenum steel material (JIS, SCM440) including no retained austenite was fatigue tested. Fatigue process was observed using a scanning Hall probe microscope in order to investigate the effect of cyclic slit opening and crack growth on residual magnetic fields. It is found that the cyclic opening-closing of the slit decreases the magnetic flux density even where no tensile stress was applied.